An electric vehicle, also referred to as an electric drive vehicle, is a moving vehicle using one or more electric motors as driving system. Not like petroleum-based transportations which are moved by the energy from burning gasoline, the electric vehicles use electric power as their propulsion. They won't generate waste gas. Noise is also less. During the last few decades, increased concern over the environmental impact of the petroleum-based transportation, along with the spectre of peak oil, has led to renewed interest in an electric transportation. Electric power for electric vehicles can be generated from a wide range of sources, including fossil fuels, nuclear power, and renewable sources such as tidal power, solar power, and wind or any combination of those.
Some of the electric vehicles or even hybrid electric vehicles are now being commercially used. A nickel-metal hydride (Ni-MH) secondary battery has been mainly used as the power source for the electric vehicles (EV) and the hybrid electric vehicles (HEV). In recent years, even the use of a lithium-ion secondary battery has been attempted. High output and large capacity are needed for such secondary batteries to provide. For this reason, many small-sized secondary batteries (unit cells) are connected in series or in parallel with each other so as to construct a battery module. Many battery modules are connected in parallel or in series with each other so as to construct a battery pack.
In such a high-output, large-capacity battery pack, however, a large amount of heat is generated from the unit cells during the charge and the discharge of the unit cells. When the heat generated from the unit cells during the charge and the discharge of the unit cells is not effectively removed, heat is accumulated in the unit cells with the result that the unit cells are degraded. Consequently, it is necessary to provide a cooling system for such battery packs.
Particularly when a battery module is used to drive a motor for a hybrid electric vehicle (HEV), it is important to have adequate heat dissipation. If heat is not dissipated properly, the heat generated from the unit cells causes a temperature variation among the unit cells. The heat generated at the unit cells may also cause the temperature inside the unit cells to increase, resulting in explosion thereof.
Since a battery module for a HEY is charged and discharged by a high current, it may have deteriorated performance due to the heat generated by the internal reaction of a rechargeable battery.
Please refer to FIG. 1. U.S. Pat. No. 7,795,845 discloses a rechargeable battery module 10 including a plurality of unit cells 11; and a housing 12 in which the unit cells 11 are mounted and in which a coolant (indicated by the arrows) for controlling the temperature in the housing 12 circulates. The unit cells 11 are disposed in the housing 12 on a slant at a predetermined angle with respect to an inflow of the coolant. The prismatic unit cells 11 are arranged at predetermined intervals inside the housing 12 to form a cell series 13. The housing 12 has an inlet 14 at one side, through which air for regulating the temperature of the unit cells 11 can flow in, and an outlet 15 at the other side thereof, through which the air passing by the unit cells 11 can dissipate. However, the intervals between the unit cells 11 can't be too small or else the coolant won't be able to circulate, and therefore, the size of the rechargeable battery module 10 is limited and can't be minimized.
Please Refer to FIG. 2. US Pub. No. 2007/0196728 discloses a battery that has a double filter device mounted at an air inlet part, through which air for cooling the battery pack. The double filter includes a pre-filter having relatively large air holes. The pre-filter has high frequency of replacement and a medium filter has relatively small air holes. The medium filter having low frequency of replacement. The pre-filter is located before the medium filter in the direction in which the air is introduced. Consequently, dust is removed from the air and the cooling efficiency of the battery pack is increased. However, such structure makes the battery bulgy which is not suitable for compact designs of battery packs.
Thus, a battery pack having an efficient cooling system which has a compact size and can also enhance the structure of the battery pack is desperately needed.